1. Field of the Invention
This invention relates generally to antennas and, more particularly, to a directional antenna used in the traffic alert and collision avoidance systems (TCAS) of aircraft avionics equipment. The antenna can transmit a directional radiation pattern to activate transponders of transponder-equipped aircraft in a vicinity of the aircraft. The antenna operating in a radiation receiving mode receives the radiation from transponder-equipped aircraft. In the preferred embodiment, the relative bearing or relative direction of the transponder-equipped intruder aircraft can be determined by comparison of the relative amplitudes of signals induced in the antenna elements of the monitoring aircraft. Typically, the two signals of greatest amplitude (in an antenna with four antenna elements) can provide the direction of an intruder aircraft, the antenna of the present invention having four antenna elements in the preferred embodiment.
2. Description of the Related Art
As technology in air transportation has evolved, the demands on the members of the flight deck have become increasingly severe. The flight deck must monitor increasing amounts of aircraft status information at a time when the air traffic is dramatically increasing. The aircraft speeds have similarly increased, reducing the time in which the flight deck can respond to threatening situations.
In order to assist the flight deck and provide an increased margin of safety in the air transport environment, several systems have been and are in the process of being developed. Aircraft are being provided with transponders (e.g., mode S, mode C, mode A, ATCRBS, etc.) by which one aircraft can communicate to a second aircraft both its identity and flight parameters. Typically, a monitoring aircraft will transmit a signal in a predetermined format which, upon receipt by an intruding aircraft will cause the intruding aircraft to respond with a transmission which includes information in a predetermined format. A series of systems have been and are being developed, generally referred to as traffic alert and collision avoidance systems (generally referred to as TCAS systems), in which the information provided to a receiving aircraft can be processed along with the status parameters of the receiving aircraft to identify potential collision situations. The traffic alert and collision and avoidance systems also provide the flight deck with advisory information suggesting an action to avoid the collision situation.
A key element in the mode S (and other) transponder systems and the traffic alert and collision avoidance systems is the directional antenna. The directional antenna is used to determine the bearing or direction of intruder aircraft relative to a TCAS-equipped monitoring aircraft. When the relative direction has been determined by the processing of radiation induced signals by the monitoring aircraft, this information can be visually displayed to the members of the flight deck and can assist them in obtaining visual contact with the intruder aircraft.
A need has therefore been felt for an antenna which can determine a direction from which radiation is being transmitted. The direction from which the radiation is being transmitted can be determined by the relative induced signal amplitudes at each of the antenna elements. In addition, the antenna should provide a minimum profile to reduce the drag associated with the antenna array, should be relatively simple to manufacture, and should be relatively impervious to environment hazards while maintaining the precise positional relationships between the antenna components.